libdaemon-jvm is a libdaemon-inspired library for the JVM written in Scala.
It aims at making it easier for JVM-based daemon processes to
- ensure that a single instance of it is running at a time
- rely on domain sockets to listen to incoming connections
libdaemon-jvm relies on Java file lock mechanism to ensure only a single instance of a process is running at a time.
More concretely, it is passed a directory, where it writes or creates:
- a lock file
- a PID file
- a domain socket
It ensures that no-two processes relying on the same directory can run at a time, relying on both the PID file and the domain socket to check for another running process.
libdaemon-jvm creates domain sockets using Unix domain socket support added in Java 16.
Add the following dependency to your build
io.github.alexarchambault.libdaemon::libdaemon:0.0.5
The latest version is 
From the server, call Lock.tryAcquire, and start accepting connections on the server socket in the thunk passed to it:
import libdaemonjvm.server._
import java.nio.file._
val daemonDirectory: Path = ??? // pass a directory under the user home dir, computed with directories-jvm for example
val lockFiles = LockFiles.under(daemonDirectory)
val res = Lock.tryAcquire(lockFiles) { serverSocket: ServerSocketChannel =>
// you should start listening on serverSocket here, and as much as possible,
// only exit this block when you are actually accepting incoming connections
}
res match {
case Left(ex: LockError.RecoverableError) => // something went wrong, you may want to retry after a small delay
case Left(ex: LockError.FatalError) => // something went wrong, retrying makes less sense here
case Right(_) => // daemon is listening on domain socket
}